The present invention relates generally to the safe storage and transfer of cryogenic fluids inside the cargo bay of a reusable launch vehicle, and more particularly to cryogenic fluid transfer systems for transferring supercritical cryogenic fluids to subcritical storage tanks in zero gravity environments, thus eliminating potential ignition hazards associated with cryogenic oxygen and hydrogen storage and management through a unique fluid transfer process in a space environment.
Cryogenic fluids such as liquid oxygen (LO2) and liquid hydrogen (LH2) are widely used by the aerospace industry as propellants, reactants for power generation, life support systems, sensor cooling, and the like. Although launch vehicles, such as the Space Shuttle, use these cryogens routinely with on-board systems, the storage and handling of these cryogens has been discouraged for payloads due to serious safety issues arising from storage and handling of cryogens inside a closed payload bay compartment. This is due to the fact that reusable launch vehicles (RLV), such as the Space Shuttle, impose unique safety requirements on cryogenic payloads because the payload must be loaded with cryogens on the ground inside a closed compartment, and the RLV must return to the ground with the payload intact in case of an aborted mission. Because the LO2 or LH2 tank is inside a closed cargo bay, serious safety issues arise during loading or after an aborted mission touchdown from small leaks and post landing venting. The concern is that a small amount of hydrogen or oxygen leakage over an extended period of time, e.g., during loading, launch, or post-touchdown, can cause a buildup of hazardous gas concentrations which can result in a fire or catastrophic explosion causing the possible loss of the space vehicle and its crew. Safety issues associated with ignition and explosion can be eliminated if the payload does not have cryogens below altitudes where ignition/explosion can occur. For hydrogen and oxygen the safe altitude where ignition does not occur is above 160,000 ft. At this altitude the atmospheric pressure is too low to support ignition, and therefore hydrogen and oxygen behaves as inert fluids like nitrogen or helium.
Because RLV""s, such as the Space Shuttle, contain cryogenic storage tanks for on-board power generation and life support systems, it is possible to transfer hydrogen or oxygen into payloads once the vehicle reaches a safe altitude where ignition hazards are eliminated and where there is sufficient time to completely dump and vacuum inert the payload storage tanks prior to landing. One source of cryogenic fluid is the supercritical storage tanks used to generate electrical power for the Shuttle. The Shuttle""s supercritical storage system consists of LO2 and LH2 tanks located in the Orbiter vehicle and also additional storage tanks located on a palette inside the cargo bay referred to as the extended duration orbiter (EDO) tanks. To eliminate liquid acquisition devices that are typically needed in a zero gravity environment, the cryogenic LH2 and LO2 is stored at super critical pressures. Consequently, the fluid is stored as a single phase fluid with no liquid vapor phase. The supercritical pressure is maintained by adding electrical heat to the tank to offset the pressure decay from fluid expulsion. Because the cryogens are stored at supercritical pressures, fluid transfer to a subcritical cannot be done directly.
The cryogenic storage tanks on the EDO pallet are typically tied into (i.e., in fluid communication with) both the fuel cells/life support systems and the pre-existing standard supercritical storage tanks in the orbiter, as shown in the configuration depicted in FIG. 1. The EDO cryogenic fluid storage system 10 typically consists of a tank 12 having a fill port 14 and a vent port 16. A conduit 18 from the vent port 16 branches off into another conduit 20 that leads to a relief valve 22 which in turn leads to a common relief line 24. Conduit 18 also branches off into another conduit 26 which leads to a shutoff valve 28 which in turn leads to a conduit 30 which is in fluid communication with the orbiter cryogenic fluid storage system 32. The orbiter cryogenic fluid storage system 32 typically consists of a tank 34 having a fill port 36 and a vent port 38. A conduit 40 from the vent port 38 leads to a shutoff valve 42 which leads to a conduit loop 44 having a check valve 46 located therein. A conduit 48 from the shutoff valve 42 leads to a vent disconnect assembly 50. Conduit 30 from vent port 16 is in fluid communication with conduit loop 44 and conduit 48. A conduit 52 from fill port 36 leads to shutoff valve 54 which leads to a conduit loop 56 having a check valve 58 located therein. A conduit 60 from the shutoff valve 62 leads to a fill disconnect assembly 62. A conduit 64 from the fill port 14 leads to a shutoff valve 66 which in turn leads to a conduit 68 which is in fluid communication with conduit 60. In order to supply cryogenic fluid to the orbiter""s fuel cells and life support systems, it is necessary to provide supply conduits from the two main sources of cryogenic fluid. The EDO cryogenic fluid storage tank 12 is provided with a conduit 70 which leads to a check valve 72 which in turn leads to a conduit 74 which is in fluid communication with the orbiter""s fuel cells and life support systems. Likewise, the orbiter cryogenic fluid storage tank 34 is provided with a conduit 76 which leads to a check valve 78 which in turn leads to a conduit 80 (which ties into conduit 74) which is also in fluid communication with the orbiter""s fuel cells and life support systems.
Therefore, there is a need for a system that permits the safe and efficient transfer of cryogenic fluids from supercritical storage systems to subcritical storage systems, especially in low g and/or zero-g vacuum environments.
The present invention provides for the safe transfer of LO2 or LH2 from the Space Shuttle supercritical tanks in a low g vacuum environment which enables cryogenic upper stages to be flown in the cargo bay of the Space Shuttle or second generation RLV. The cryogens that can be transferred to a payload cryogenic tank may be used to demonstrate long term cryogenic fluid management, power upper stages, and provide reactants for power generation, cool sensors or electronic equipment.
It is therefor an object of the present invention to provide a new and improved cryogenic fluid transfer system.
It is another object of the present invention to provide a new and improved cryogenic fluid transfer system for use in zero gravity environments.
It is still another object of the present invention to provide a new and improved cryogenic fluid transfer system for transferring a cryogenic fluid from a supercritical cryogenic fluid storage system to a subcritical cryogenic fluid storage system.
In accordance with one embodiment of the present invention, a cryogenic fluid transfer system for transferring a cryogenic fluid from a supercritical cryogenic fluid storage system is provided, comprising:
a first subcritical cryogenic fluid storage system for receiving the cryogenic fluid from the supercritical cryogenic fluid storage system;
a conduit for providing fluid communication between the supercritical cryogenic fluid storage system and the first subcritical fluid storage system; and
a heat exchanger assembly in contact with the conduit, the heat exchanger assembly located downstream of the supercritical cryogenic fluid storage system and upstream of the first subcritical fluid storage system;
wherein the heat exchanger assembly cools the cryogenic fluid expelled from the supercritical cryogenic fluid storage system prior to the cryogenic fluid being introduced into the first subcritical fluid storage system.
In accordance with another embodiment of the present invention, a cryogenic fluid transfer system is provided, comprising:
a supercritical cryogenic fluid storage system;
a first subcritical cryogenic fluid storage system for receiving the cryogenic fluid from the supercritical cryogenic fluid storage system;
a conduit for providing fluid communication between the supercritical cryogenic fluid storage system and the first subcritical fluid storage system;
a heat exchanger assembly in contact with the conduit, the heat exchanger assembly located downstream of the supercritical cryogenic fluid storage system and upstream of the first subcritical fluid storage system;
wherein the heat exchanger assembly cools the cryogenic fluid expelled from the supercritical cryogenic fluid storage system prior to the cryogenic fluid being introduced into the first subcritical fluid storage system; and
a source of pressurized inert gas in fluid communication with the first subcritical fluid storage system, wherein the source of pressurized gas permits the pressurization of the first subcritical cryogenic fluid storage system.
In accordance with still another embodiment of the present invention, a cryogenic fluid transfer system is provided, comprising:
a supercritical cryogenic fluid storage system;
a first subcritical cryogenic fluid storage system for receiving the cryogenic fluid from the supercritical cryogenic fluid storage system;
a second subcritical fluid storage system for receiving the cryogenic fluid from the supercritical cryogenic fluid storage system or the first subcritical cryogenic fluid storage system;
a conduit for providing fluid communication among the supercritical cryogenic fluid storage system and the first and second subcritical fluid storage systems;
a heat exchanger assembly in contact with the conduit, the heat exchanger assembly located downstream of the supercritical cryogenic fluid storage system and upstream of the first and second subcritical fluid storage systems;
wherein the heat exchanger assembly cools the cryogenic fluid expelled from the supercritical cryogenic fluid storage system prior to the cryogenic fluid being introduced into the first or second subcritical fluid storage systems;
a source of pressurized inert gas in fluid communication with the first and second subcritical fluid storage systems, wherein the source of pressurized gas permits the pressurization of the first and second subcritical cryogenic fluid storage systems; and
a gaseous fluid source in fluid communication with the first and second subcritical fluid storage systems and the supercritical cryogenic fluid storage system.
Additional objects, advantages, and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.